3GPP (3rd Generation Partnership Project), which is a standardization project for W-CDMA (Wide-band Code Division Multiple Access) wireless communication systems, has promoted standardization of HSDPA (High Speed Downlink Packet Access) schemes which are packet transmission schemes designed to increase the transmission rates of downlinks from wireless base stations to mobile communication devices such as cellular phones. This HSDPA scheme uses an HS-PDSCH (High Speed-Physical Downlink Shared Channel) and an HS-SCCH (High Speed-Shared Control Channel of HS-PDSCH) as downlink physical channels. An HS-PDSCH is used to transmit packet data and shared by a plurality of mobile communication devices. An HS-SCCH is used to transmit information associated with H-ARQ (Hybrid-Automatic Repeat Request which is an encoding scheme based on a combination of an error correction technique and an automatic retransmission request technique) control and the layer 1 information (the physical channel of the OSI protocol) of an HS-PDSCH such as TFRI (Transport-Format and Resource Related Information).
An HS-DPCCH (High Speed-Dedicated Physical Control Channel) is an uplink physical channel defined in the HSDPA scheme. This HS-DPCCH is used to transmit response information for the above H-ARQ and a CQI (Channel Quality Indicator: reception quality information). In this case, reception quality information is obtained by measuring the quality of a CPICH (Common Pilot Channel) signal. This reception quality information represents the communication state of a propagation path between a mobile communication device and a wireless base station, and is used to determine the encoding rate of data to be transmitted to a mobile communication device via an HS-PDSCH. In addition, quality is represented by Ec/Io (energy per chip/interference power per unit frequency).
Conventionally, as shown in FIG. 6, a cellular telephone conforming to this HSDPA scheme comprises an antenna 1, a duplexer (DUP) 2, a reception unit 3, a demodulation unit 4, a de-spreading unit 5, a reception power calculation unit 6, a buffer 7, an SIR calculation unit 8, a CQI selection unit 9, a multiplexer (MUX) 10, modulation units 11 and 12, a multiplexer (MUX) 13, and a transmission unit 14.
In this cellular phone, the reception unit 3 receives a reception radio wave Wa via the antenna 1 and the duplexer 2, and the reception result is separated into an HS-PDSCH (High Speed-Physical Downlink Shared Channel)/DPCH (Dedicated Physical Channel) including user information, an HS-SCCH (High Speed-Shared Control Channel)/CPICH (Common Pilot Channel) including control information, and the like. The demodulation unit 4 demodulates the HS-PDSCH, HS-SCCH, and DPCH into reception packet data, control information, and the like and outputs them.
Of the control information, CPICH information is used for the measurement/calculation of the power of a downlink signal from a wireless base station, and is used for the creation of a CQI (reception quality information). In creating a CQI, first of all, the de-spreading unit 5 performs de-spreading processing for each symbol (e.g., eight bits) of a CPICH, and the reception power calculation unit 6 calculates ISCP/RSCP at a predetermined TTI (Transmission Time Interval) corresponding to the HSDPA scheme. The buffer 7 buffers (stores) the obtained ISCP/RSCP until ISCP/RSCP corresponding to a CQI creation reference section is stored. Thereafter, the SIR calculation unit 8 calculates an SIR (Signal to Interference Ratio) by using the ISCP/RSCP corresponding to the CQI creation reference section. The CQI selection unit 9 creates a CQI on the basis of the calculation result.
The multiplexer (MUX) 10 multiplexes the CQI with other control information. The modulation unit 11 performs spread spectrum modulation of the resultant information using a local spreading code. The multiplexer (MUX) 13 multiplexes the resultant information with user information, control information, and the like which are spread-spectrum-modulated by the modulation unit 12 using a local spreading code to obtain information on an HS-DPCCH as an uplink channel. The transmission unit 14 converts the multiplexed information into a transmission signal and transmits it as a transmission radio wave Wb from the antenna 1 via the duplexer 2.
In addition to the above cellular phone, other techniques of this type are disclosed in, for example, the following references.
The communication terminal device disclosed in reference 1 (Japanese Patent Laid-Open No. 2005-057710) creates reception quality information (a temporary CQI) representing different reception qualities depending on whether a measurement value (SNR) representing the reception quality measured from a reception signal is equal to or more than a threshold or less than the threshold. This device also creates the probability density distribution of reception quality information by using the created reception quality information, and also calculates a median which is reception quality information indicating the maximum value of the probability densities of the created probability density distribution. The device then corrects the reception quality information on the basis of the difference between the calculated median and the reception quality information, thereby determining reception quality information (a report CQI) to be reported to a base station apparatus.
The communication device having the communication quality control function disclosed in reference 2 (Japanese Patent Laid-Open No. 2005-064963) reports, to a base station, feedback information created on the basis of a measurement result on channel quality. This device counts the number of times data blocks transmitted with the transmission parameter determined by the base station are normally or abnormally received, while assigning a weight corresponding to a likelihood predicted from the difference between feedback information and the transmission parameter actually used for transmission, and updates a channel quality threshold corresponding to the feedback information in accordance with the count value. This can create feedback information transmitted with a transmission parameter suitable for actual transmission characteristics and perform adaptive encoding modulation which keeps high communication quality constant even if the propagation environment is not constant or previously reported feedback information differs from the transmission parameter actually transmitted from the base station.